Two methods are commonly used for casting concrete blocks: wet casting and dry casting. In a wet casting process, liquid concrete is poured into a block form cavity and remains in the cavity until the concrete has cured sufficiently to permit removal without damage to the cast block. During the cure time, the form cannot be used for casting additional blocks. When one or more surfaces of the block are to be decorative, one or more walls of the cavity may be lined with, for example, a urethane liner shaped to impart a desired texture or decoration to the cast block. This process may be used, for example, to form concrete blocks simulating natural stone with deep irregular fissures.
In a typical dry casting process, a form having an open top and an open bottom is places on a rigid support surface such as a pallet. The form is then filled to a desired level with a relatively dry cement mixture, which is not as fluid as in the cement used in wet casting. The cement mixture is then pressed into the form cavity with sufficient pressure to form a block which has sufficient rigidity to hold its shape when the form is removed. The block is then transferred to a curing station and the form can be immediately reused for casting additional blocks. The dry casting process is commonly used for casting concrete building foundation and wall blocks. However, it has in the past only been suitable for producing blocks having a decorative surface having a relatively shallow texture or pattern. Deeper patterns have not been achievable due to problems with the relatively soft uncured block breaking when separating the block from the mold which forms the decorative surface.
In operating prior art dry casting block machines, the forms have been provided with either straight sides or with a slight relief angle so that the form can be separated from the uncured blocks without breaking the blocks. This has prevented use of the forms for imparting projections and notches on the sides of the blocks.